1. Field of the Invention
The invention relates to an identification technique that allows an electrical circuit to be communicatively associated with a particular external entity using a random identifier code that is derived from signal data produced by the circuit.
2. Description of the Related Art
In wired communications, a sending device (such as a mouse or keyboard) is cabled to its corresponding receiver. The receiver receives data from the sending device via the cable or other physical interface means, and communicates that data to its intended destination (such as to a computer motherboard). Thus, the communicated data is generally only reported to its intended destination. However, in wireless communications, there is no physical connection between the sending device and the receiving device. Commonly, in any given work area where wireless communications are taking place, there can be multiple transmitter-receiver pairs. In such a work area, any one receiving device can receive multiple transmissions from a number of sending devices. Various techniques have evolved to deal with such a signal rich environment to ensure that each transmitted signal is received by the intended receiver.
One such technique is to simply allow the transmitted signals to be received by multiple receivers that are present in the environment. So long as the transmitted signal is received by the correct receiver, the wireless communication will be effective. However, it is possible that other receivers in the environment that also receive the transmitted signal may erroneously report that signal. For example, consider two wireless mouse-receiver pairs employing this technique, one pair operating at a first workstation and the second pair operating at a nearby second workstation. It is possible that the mouse of the first workstation will be able to control the cursor of the second workstation because the receiver of the second workstation cannot tell the difference between the transmissions of its own mouse and the transmissions of the first workstation's mouse. Thus, this technique may be undesirable, for example, because of the general interference as well as security issues (e.g., remotely controlling the local cursor) associated with multiple transmitter-receiver pairs.
Another technique to ensure that each transmitted signal is received by the appropriate receiver involves establishing an identifier that is associated with any one receiver-transmitter pair. This technique reduces the likelihood of interference and security risks associated with the technique previously described. The identifier is embedded in the signal transmitted from the sending device. Such an identifier, for example, may be a multiple bit code. The corresponding receiving device will only accept, report on, or otherwise react to received signals containing the correct identifier code. Signals received by the receiving device that do not contain the appropriate identifier code are ignored. Thus, there is no erroneous reporting by the receiving device. However, this technique requires that a predefined identifier be stored in the transmitting device.
More specifically, a read-only memory (ROM) type device (e.g., electronically erasable programmable ROM or EEPROM) is used for storing the predefined identifier. For instance, during the manufacturing process of the transmitter-receiver pair, a predefined identifier code is programmed into the EEPROM. The predefined identifier code will then be available when the sending device transmits data. This EEPROM adds substantial cost (e.g., approximately 30 cents per unit) due to the EEPROM itself, the manufacturing process involved in placing and programming the EEPROM, and the physical space consumed by the EEPROM.
What is needed, therefore, is a technique that allows for a transmitter and receiver to be associated with one another by an identifying code. The technique should not require an additional memory module (such as an EEPROM) to be installed during the manufacturing process for storing a pre-assigned identifying code. Additionally, the technique should assign identifier codes to transmitter-receiver pairs in a random fashion.